One of the many challenges faced during continuous scaling of integrated circuits (ICs) is to achieve acceptable electromigration (EM) reliability for Cu interconnects. One way to address this challenge is the deposit of a metallic capping layer on Cu upper interface. The electroless deposition of cobalt tungsten phosphide (CoWP) appears to be the most promising candidate as a capping layer for Cu metallization.
The successful implementation of CoWP depends, not only on an optimized deposition, but also on a complete CoWP compatible integration processing, which includes wet clean processing. However, the common semi-aqueous fluoride strippers and diluted hydrofluoric acid (DHF) strippers are incompatible with CoWP, which completely remove the CoWP layer during the wet clean process.
See J. Lauerhaas, Reduced Oxygen Cleaning Process for Advanced Cu/Low-k Integration, SEMATECH Surface Preparation and Cleaning Conference, Mar. 23-25, 2009.
The present invention discloses wet clean formulations which demonstrate proficient cleaning on CoWP exposed patterned wafers, while maintaining CoWP integrity, as will be disclosed more fully below.